Movie deals with tricking nature of two basic corner stones of our mind: memory and imagination. Invented past as anchor for future. But lately research shows that the same brain structures are responsible for memories and imagination. And that believing can be seeing – Context Dictates What We Believe We See. Pretty visionary movie though.

“You might look at it as mental time travel–the ability to take thoughts about ourselves and project them either into the past or into the future,” says Kathleen McDermott, Ph.D. and Washington University psychology professor. The team used “functional magnetic resonance imaging” — or fMRI — to “see” brain activity. They asked college students to recall past events and then envision themselves experiencing such an event in their future. The results? Similar areas of the brain “lit up” in both scenarios.

Researchers say besides furthering their understanding of the brain — the findings may help research into amnesia, a curious psychiatric phenomenon. In addition to not being able to remember the past, most people who suffer from amnesia cannot envision or visualize what they’ll be doing in the future — even the next day.”

Another good article, posted in Scientific American Mind, uses Memento to explain the nature of memory.

The Matrix in Your Head

In the 2001 suspense thriller Memento, the lead character, Lenny, suffers a brain injury that makes him unable to remember events for longer than a minute or so. This type of amnesia, known as anterograde amnesia, is well known to neurologists and neuropsychologists. Like Lenny, sufferers remember events from their life histories that occurred before their injuries, but they cannot form lasting memories of anything that occurs afterward. As far as they recall, their personal histories ended shortly before the onset of their disorders.

The cause of Lenny’s problem was probably damage to his hippocampus, a pair of small, deep-brain structures crucial to memory—and also important to some of today’s most exciting and consequential neuroscience research. Decades of research have made clear that the hippocampus and surrounding cortex do more than just place our life events in time. The hippocampus, along with a newly discovered set of cells known as grid cells in the nearby cortex, traces our movement through space as well. And by doing so, it supplies a rich array of information that provides a context in which to place our life’s events. The picture that is emerging is of historic importance and more than a little beauty.

Exactly how does the brain create and store autobiographical memories? Although that question has fascinated scientists, philosophers and writers for centuries, it was only 50 years ago that scientists identified a brain area clearly necessary for this task—the hippocampus. The structure’s role was made clear in 1953, when William Scoville, a Hartford, Conn., surgeon seeking to relieve the epileptic seizures that were threatening to kill a patient known as H.M., removed most of H.M.’s hippocampus and discovered he had rendered him unable to form new, conscious memories. Since then, the case of H.M., along with extensive animal research, has firmly established that the hippocampus acts as a kind of encoding mechanism for memory, recording the timeline of our lives.

In the 1970s another discovery inspired the theory that the hippocampus also encodes our movement through space. In 1971 John O’Keefe and Jonathan Dostrovsky, both then at University College London, found that neurons in the hippocampus displayed place-specific firing. That is, given “place cells,” as O’Keefe dubbed these hippocampal neurons, would briskly fire action potentials (the electrical impulses neurons use to communicate) whenever a rat occupied a specific location but would remain silent when the rat was elsewhere. Thus, each place cell fired for only one location, much as would a burglar alarm tied to a tile in a hallway. Similar findings have been reported subsequently in other species, including humans.

These remarkable findings led O’Keefe and Lynn Nadel, now at the University of Arizona, to propose that the hippocampus was the neural locus of a “cognitive map” of the environment. They argued that hippocampal place cells organize the various aspects of experience within the framework of the locations and contexts in which events occur and that this contextual framework encodes relations among an event’s different aspects in a way that allows later retrieval from memory. Yet a consensus is emerging that the hippocampus does somehow provide a spatial context that is vital to episodic memory. When you remember a past event, you remember not only the people, objects and other discrete components of the event but also the spatiotemporal context in which the event occurred, allowing you to distinguish this event from similar episodes with similar components. But How?

Despite intensive study, however, the precise mechanisms by which the hippocampus creates this contextual representation of memory have eluded scientists. A primary impediment was that we knew little about the brain areas that feed the hippocampus its information. Early work suggested that the entorhinal cortex, an area of cortex next to and just in front of the hippocampus, might encode spatial information in a manner similar to that of the hippocampus, though with less precision.

This view has now been turned upside down with the amazing discovery of a system of grid cells in the medial entorhinal cortex, described in a series of recent papers by the Norwegian University of Science and Technology’s Edvard Moser and May-Britt Moser and their colleagues. Unlike a place cell, which typically fires when a rat occupies a single, particular location, each grid cell will fire when the rat is in any one of many locations that are arranged in a stunningly uniform hexagonal grid—as if the cell were linked to a number of alarm tiles spaced at specific, regular distances. The locations that activate a given grid cell are arranged in a precise, repeating grid pattern composed of equilateral triangles that tessellate the floor of the environment.

Imagine arranging dozens of round dinner plates to cover a floor in their optimal packing density, such that every plate is surrounded by other, equidistant plates; this arrangement mimics the triggering pattern tied to any given grid cell. As the rat moves around the floor, a grid cell in its brain fires each time the rat steps near the center of a plate. Other grid cells, meanwhile, are associated with their own hexagonal gridworks, which overlap each other. Grids of neighboring cells are of similar dimensions but are slightlyoffset from one another.

These grid cells, conclude the Mosers and their co-workers, are likely to be key components of a brain mechanism that constantly updates the rat’s sense of its location, even in the absence of external sensory input. And they almost certainly constitute the basic spatial input that the hippocampus uses to create the highly specific, context-dependent spatial fi ring of its place cells.

This discovery is one of the most remarkable findings in the history of single-unit recordings of brain activity.

JAMES J. KNIERIM is associate professor of neurobiology and anatomy at the University of Texas Medical School at Houston, where he studies the role of the hippocampus and related brain structures in spatial learning